PR131PR131 Tests of Spectrometers and Tests of Spectrometers and

Spectrometers and Spectrometers and DosemetersDosemeters for the Investigation of the for the Investigation of the

Radiation Environment onboard Radiation Environment onboard Spacecraft and around Spacecraft and around

HighHigh--Energy AcceleratorsEnergy Accelerators

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Günther Reitz, Thomas Berger Deutsches Zentrum für Luft- und Raumfahrt (DLR), Germany

Les Bennet Royal Military College of Canada (RMC), Canada

Martin Smith Bubble Technologies, Inc. (BTI), Canada

Burkhard Wiegel, Marlies Luszik-Bhadra, Stefan Rottger, Ralf Nolte, Volker Dangendorf Physikalisch-Technische Bundesansalt (PTB), Germany

Ricky Smit, Zinhle Buthelezi iThemba Laboratories (TLABS), South Africa

Andy Buffler, Saalih Allie, Rudolph Nchodu University of Cape Town (UCT), South Africa

… with interest from the National Metrology Laboratory of South Africa

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A. Buffler, F.D. Brooks, M.S. Allie, P.J. Binns, V. Dangendorf, K.M. Langen, R. Nolte and H. Schuhmacher, “Measurement of neutron energy spectra from 15-150 MeV using stacked liquid scintillators”, Nuclear Instruments and Methods A 476 (2002) 181-185R. Nolte, M.S. Allie, P.J. Binns, F.D. Brooks, A. Buffler, V. Dangendorf, J.P. Meulders, H. Schuhmacher, B. Wiegel , “High energy neutron reference fields for the calibration of detectors used in neutron spectrometry” Nuclear Instruments and Methods A 476 (2002) 369-373R. Nolte, M.S. Allie, P.J. Binns, F.D. Brooks, A. Buffler, V. Dangendorf, K. Langen, J.P. Meulders, W. Newhauser, F. Roos & H. Schuhmacher, “Measurement of 235U, 238U, 209Bi and natPb fission cross sections using quasi- monoenergetic neutrons with energies from 30 MeV to 150 MeV”, Journal of Nuclear Science and Technology, Supplement 2 (August 2002) 311-314F.D. Brooks, M.S. Allie, A. Buffler, V. Dangendorf, M.S. Herbert, S.A. Makupula, R. Nolte and F.D. Smit, “Measurement of neutron fluence spectra up to 150 MeV using a stacked scintillator neutron spectrometer”, Radiation Protection Dosimetry 110 (2004) 151-155R. Nolte, M.S. Allie, R. Bottger, F.D. Brooks, A. Buffler, V. Dangendorf, H. Friedrich, S. Guldbakke, H. Klein, J.P. Meulders, D. Schlegel, H. Schuhmacher and F.D. Smit, “Quasi-monoenergetic neutron reference fields in the energy range from thermal to 200 MeV”, Radiation Protection Dosimetry 110 (2004) 97-102R. Nolte, V. Dangendorf, A. Buffler, F.D. Brooks, J.P. Slabbert, F.D. Smit, M. Haney, E. Schmid, G. Stephan, “RBE of 200 Mev neutron radiation for the induction of chromosodal aberration in human lymphocytes”, In proceedings of International Workshop on Fast Neutron Detectors and Applications (Cape Town, 2-6 April 2006) Proceedings of Science (FNDA2006) 082F.D. Brooks, A. Buffler, M.S. Allie, M.S. Herbert, F.D. Smit, R. Nolte, V. Dangendorf, “A compact high-energy neutron spectrometer” , Radiation Protection Dosimetry in press (2006)

UCTUCT--PTBPTB--iTL iTL jointjoint neutron publications neutron publications 2002 2002 -- presentpresent

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… the experimental characterization of five different instruments which have been designed for the investigation of neutron energy distributions in extreme environments or used for the routine monitoring of the exposure to personnel.

Objectives of PR131Objectives of PR131

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Ambient HighAmbient High--Energy Radiation FieldsEnergy Radiation Fields• Sources of primary high-energy

charged particles: - galactic cosmic rays (GCR): p,α, HI - accelerator beams: p, HI

• Interaction with matter produces complex radiation fields: γ, e, μ, π, n, p, HI

• Neutron component extends from meV to GeV range

• Personnel exposed to such fields can receive considerable doses: - flight crews - astronauts - accelerator staff

• Neutrons contribute significant fractions to dose equivalent: 10% - 50%

Example: electromagnetic and hadronic shower produced by

GCR in the atmosphere

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Neutron Dosimetry around AcceleratorsNeutron Dosimetry around Accelerators• Dose Equivalent per unit fluence is a strong function of neutron energy

⇒ Neutron spectrum has to be known• Monte Carlo codes (FLUKA, MCNPX) still suffer from

insufficient nuclear models for the high-energy part• Very conservative (factor of two) assumptions

for design of shields: ⇒ higher costs for accelerator projects

400 MeV/u 12C10-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 100 101 102 103 1040

10

20

30

40

50

60

70

80

90

100

1

10

100

1000

400 MeV/u 12C on thick C targetneutron spectrum behind thick concrete shield

FLUKA prediction NEMUS solution

ΦE

(En) ⋅

En /

(cm

2 1010

ions

)-1 ⎯

→

En / MeV ⎯→

dose equivalent per unit fluence

H*(

10)/Φ

/ pS

v cm

2

Shielding experiment at GSI

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Neutron Dosimetry onboard Space CraftNeutron Dosimetry onboard Space Craft

• Dose values in low earth orbits exceed that found on earth by a factor of hundred - dominating contribution from charged particles - estimates for neutron component: 10 % - 30%

• Strong variation of dose rates due to - solar cycle - position of the space craft on the orbit - varying thickness of the shell

• Dose records for astronauts are a legal requirement ! Very important for long term and interplanetary missions

• Future needs– More accurate and reliable data – New detectors– Characterisation and cross-calibration of

instruments– Benchmarking of Monte Carlo models– Reduction of uncertainties in risk assessment

THE MATROSHKA ProjectTHE MATROSHKA Project

MATROSHKA data will include :Skin dose measurementsMeasurement of depth dose distributions inside the phantomMeasurements at the positions of selected organs(e.g. eye, lung, stomach..) Assessment of organ dosesBenchmarking for model calculationsImproved radiation risk estimates for long durationspaceflights

MATROSHKA is an ESA project under the scientific and project lead of the German Aerospace Centre, DLR, Cologne (Reitz).

It is designed to determine the radiation exposure of an astro – cosmonaut inside and outside the ISS using a human phantom torso equipped with active and passive radiation sensors.

It is the biggest international project in human space radiation research (in the phase 2 of MATROSHKA we have 19 partners from 11 countries).

THETHE MATROSHKA Set UpMATROSHKA Set UpAnthropomorphic phantom (33 slices)

Poncho and hood (for skin dose measurements)

Carbon fibre container (to simulate the astronaut suit)

Multi layer insulation.

Detectors:7 active radiation detectors (Univ. Kiel, Germany, NASA, Houston)

TLDs and CR-39 detectors as well as active scintillators for organ dose measurements

TLDs at 800 measurement points to measure depth dose distribution

Over 6000 passive radiation detectors

THE MATROSHKA THE MATROSHKA TimetableTimetable

MATROSHKA 1

Outside exposure for 540 days

February 2004 – August 2005

Dose rate outside 1.3 mSv/day3 times higher than inside the ISS

MATROSHKA 2 Phase A/B and C

Phase A and B inside exposures

Phase A : 2006

Phase B : 2007

Phase C : 2nd outside exposure in a different phase of the solar cycle : 2008

MATROSHKAMATROSHKA –– DetectorDetector CalibrationCalibrationThe ICCHIBAN Project - AIM

Compare response and sensitivity of various space radiation monitoring instruments.

Aid in reconciling differences in measurements made by various radiation instruments during space flight.

ICCHIBAN Runs

Up to now 10 runs with heavy ions and protons from 2002 – 2005Irradiations in well-characterised (quasi-) monoenergetic neutron beams required for:

determination of the energy dependenceverification of Monte Carlo calculations

O400, Fe3007th ICCHIBAN Experiment (For Active Detectors)

Sep. 13-17, 2005

p1000, O1000, Fe1000

1st NSRL ICCHIBAN Experiment (For All Detectors)

Sep. 24-26, 2004

8th ICCHIBAN Experiment (For Passive Detectors)

6th ICCHIBAN Experiment(For Passive Detectors)

5th ICCHIBAN Experiment (For Active Detectors)

1st Proton ICCHIBAN Experiment (For All Detectors)

4th ICCHIBAN Experiment(For Passive Detectors)

3rd ICCHIBAN Experiment (For Active Detectors)

2nd ICCHIBAN Experiment(For Passive Detectors)

1st ICCHIBAN Experiment (For Active Detectors)

He150Feb. 14-17, 2004

C135, Ar500, Kr400, …June 4-15, 2004

p70-250Sep. 6-7, 2003

He150, O400, Ar500, Fe200

Sep. 13-17, Oct. 22, 2005

He150, C400, Ne400, Fe500

May 19-30, 2003

Si800, Fe500Feb. 3-6, 2003

He150, C400, Si490, Fe500

May 23-28, 2002

C400, Fe400Feb. 11-13, 2002

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Types of space radiation• neutrons (detected by primary scintillator)• cosmic rays (vetoed by plastic scintillator)• γ

rays (pulse shape discrimination)

Visco-elastic scintillator • xylene + naphthalene• good n-γ

discrimination• isotropic response• reliable cross-sections (En < 20 MeV!)Data analysis• Unfolding using SVD technique with a response matrix

for an NE213 detector of same size

CHENSS: principle of operationCHENSS: principle of operation

scattered neutron

neutron

cosmic ray

recoilproton

Aim is to improve radiation dosimetry in space by accurately measuring the neutron fluence and energy distribution

measure and predict radiation dose to astronauts optimize radiation shielding scenarios

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Total weight = 84.5 kg = 185 lbs

Batteries20 kg

Base20 kg

Top18 kg

Pressurevessel10kg

Cylindricalsupport4 kg

Electronics + wiring10 kg

Experimentalmounting plate

Visco-elasticscintillator

Phototubes

Scintillatingsidepanels2.5 kg

G. Jonkmans et. al., Acta Astronautica 56, 975 (2005), M.B. Smith et. al., proceedings of "International Workshop on Fast Neutron Detectors and Applications" PoS(FNDA2006)006

CHENSS designed for NASA GAS can experimentsCHENSS designed for NASA GAS can experiments

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Shape (channels)

En

erg

y (c

han

nel

s)

5 MeV

0 10 20 30 40 50 600

50

100

150

200

250

0

1

2

3

4

Shape (channels)

En

erg

y (c

han

nel

s)

2.5 MeV

0 10 20 30 40 50 600

50

100

150

200

250

-1

0

1

2

3

4

5

Shape (channels)

En

erg

y (c

han

nel

s)

14.8 MeV

0 10 20 30 40 50 600

50

100

150

200

250

0

1

2

3

4

5

6

Shape (channels)

En

erg

y (c

han

nel

s)

19 MeV

0 10 20 30 40 50 600

50

100

150

200

250

-2

-1

0

1

2

3

4

5

n

γ

3H(p,n)3He 2H(d,n)3He

3H(d,n)4He 3H(d,n)4He

LowLow--energy calibration at PTBenergy calibration at PTB

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The Bonner Sphere Spectrometer NEMUSThe Bonner Sphere Spectrometer NEMUS

• 10 PE moderator spheres: ∅

3" - ∅

12" • 4 PE moderator spheres with Cu and Pb inserts• 3He prop. counter (low to moderate flux densities)• Ag foil+PIPS detector under development (high flux density)

2 4 6 8 10 120

1

2

3

4

5

count rate vs. diameter

b-Cd

bare

Nd /

a.u.

⎯→

d / (2,54 cm) ⎯→

Bonner Sphere Spectrometer:

• therm. to several 100 MeV neutrons

• high sensitivity

• almost isotropic response

• pulsed and unpulsed fields

• needs: - pre-information on spectrum - sophisticated data analysis

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Solution Φ(E) maximizes relative information entropy

under the constraints

Data Analysis: FewData Analysis: Few--Channel UnfoldingChannel Unfolding

• Reponse calculated using MCNPX– En < 150 MeV: evaluated cross

section (ENDF/B-VI)– En > 150 MeV: Intra-Nuclear

Cascade Model

• Data analysis: Inverse problem

MAXED code

dEEEE

EES DEFDEF∫

⎭⎬⎫

⎩⎨⎧

Φ−Φ+⎟⎟⎠

⎞⎜⎜⎝

⎛ΦΦ

Φ−= )()()(

)(ln)(

10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 100 101 102 103 1040

1

2

3

4

5

6

7

8

9

10

bare 3He proportional counter 3" PE sphere to 12" PE sphere 3P5_7 (lead) 4C5_7 (copper) 4P5_7 (lead) 4P6_8 (lead)

Rd(E

n) / c

m2 ⎯

→En / MeV ⎯→

Ω=⎟⎟⎠

⎞⎜⎜⎝

⎛σε

Φ⋅=ε+ ∑∫2

;d)(d d

dddd EERN

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NEMUS CalibrationNEMUS Calibration

• Efficiency of the 3He det. measured relative 197Au(nth ,γ)

• Tests of calculated response using (quasi-) monoenergetic neutrons PTB: 25 meV, 1.7 keV - 19 MeV UCL: 60 MeV

• Overall renormalisation: 2% (H/C = 2 ?)

⇒deviations < 5%!

• Higher energies important because uncertainty of MC calculation increases: TLABS: 100 MeV, 200 MeV

3P5_

74C

5_7

4P5_

74P

6_8

3P5_

74C

5_7

4P5_

74P

6_8

3P5_

74C

5_7

4P5_

74P

6_8

0,85

0,90

0,95

1,00

1,05

1,10

1,15

60 MeV19 MeV

Rca

lc /

Rm

eas

sphere label

2.5 MeV

2 4 6 8 10 120.90

0.92

0.94

0.96

0.98

1.00

1.02

1.04

Rca

lc /

Rm

eas

sphere label

f = 1.022

PE spheres

PE+metal spheres

?

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Beam characterisationBeam characterisation

• NE213 detector + TOF: → ΦE /Φ0

• 238U PPFC + TOF: → ΦE , Φ0

• Beam Monitors:– current– thin NE102 detector– 238U fission chamber

• Beam size: 12.5 cm x 12.5 cm @ 10 m

⇒Scanning machine required– remote control– step scan, pseudo-Lissajous scan– coupled with DAQ– virtual field size < 60 cm x 60 cm

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SummarySummary… iTL neutron beam facility provides beams of quasi-monoenergetic neutrons which have now been well characterized.… the UCT-PTB collaboration have developed reliable techniques for the measurement of spectral neutron fluence over a wide energy range (30 – 200 MeV) … and a strong track record wrt output.… this provides opportunities for interesting physics and instrumentation development (recent work has been very successful)… the present work brings a high profile collaboration to iTL with opportunities for new links for the lab and new partnerships for the UCT-PTB-iTL neutron collaboration.

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SpinSpin--offs ...offs ...

… apart from the usual research activities (opportunities for student involvement, academic exchange, scientific papers, … ) … UCT-PTB is a strong collaboration …… significant possibilities for positive publicity for iThemba LABS … “iThemba LABS calibrates instruments for the International Space Station” …… involvement of NML (South Africa) and PBMR (?) … state-of-the-art neutron detection systems coming to iThemba LABS … opportunities for technology transfer …

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Beam time requestBeam time request

ns-pulsed neutron beamsNo additional costs to iTL... use existing D-line infrastructure

Request made for 3 weekends (not 2).Weekend 1: 100 MeVWeekend 2: 200 MeVWeekend 3: Reserve or 63 MeV or ...

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QuasiQuasi--monoenergeticmonoenergetic neutronsneutrons are obtained either:are obtained either: (a) by selecting the TOF peak (if (a) by selecting the TOF peak (if ΔΔt < few ns)t < few ns); or; or (b) by using the (0(b) by using the (0°° and 16and 16ºº) difference method. ) difference method.

Neutron spectra (measured by TOF), from 100 MeV protons on a natLi target:

Spectral neutron fluence, normalised to the same number of protons

0 10 20 30 40 50 60 70 80 90 100 1100

1

2

3

4

5

6

7

natLi(p,n): 0° 16°

Φ E /

Nm

on (a

rb. s

cale

)

En / MeV0 20 40 60 80 100

0

1

2

3

4

5

6

natLi(p,n): difference beam

ΦE /

Nm

on (a

rb. s

cale

)En / MeV